Non-plated aluminum based bearing alloy with performance-enhanced interlayer

ABSTRACT

A bi-metal aluminum includes bearing an aluminum-based bearing layer, a steel backing, and an intermediate aluminum-based layer that has a thickness of from 60 to 120 micrometers positioned between the aluminum-based bearing layer and the steel backing. The intermediate layer has a yield strength that is less than that of the aluminum-based bearing layer. The aluminum-based bearing layer has a fine microstructure which imparts a very high fatigue strength. The aluminum bearing layer generally includes 4% to 15% by weight lead or tin, up to 26% by weight silicon and up to 2% by weight of any of the elements magnesium, manganese, nickel, zirconium, zinc, copper, or chromium with the remainder of the bearing layer being aluminum.

[0001] This invention is disclosed in provisional patent application60/248,931, filed Nov. 15, 2000, whose priority is claimed for thisapplication.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates generally to multi-layer slidingbearings of the type having two or more metal layers bonded to a steelbacking strip for use in journaling a shaft or the like.

[0004] 2. Related Art

[0005] Sleeve or sliding bearings for use as main bearings or connectingbearings in internal combustion engines can be divided into two maincategories. The categories: (1) bimetal bearings, which consist of asteel backing and a lining alloy on the inside diameter; (2) trimetalbearings, which include a third layer which is typically electrodeposited over the lining alloy.

[0006] Bimetal bearings typically include an aluminum based liningmaterial placed on the inside diameter of a bearing. This type ofbearing offers advantages over trimetal bearings including low cost,good wear resistance, and excellent corrosion resistance. However, formore severe applications, such as in today's higher output engines,there is a need for a bearing with a high fatigue strength and excellentsliding properties which cannot be achieved utilizing bimetal bearingshaving an aluminum based lining. Typically, trimetal bearings whichexhibit a higher fatigue strength than most bimetal bearings must beutilized in the more severe applications.

[0007] Several factors known in the art for improving the fatiguestrength and performance of bearings include: (a) inclusion of a softphase, such as tin or lead within the alloy layer to impart seizureresistance to the lining alloy; (b) inclusion of hard particles withinthe aluminum alloy such as silicon to increase the wear and seizureresistance of the alloy; (c) inclusion of an interlayer between thealuminum bearing alloy and the steel backing to achieve bonding betweenthe lining and the steel when the amount of the soft phase exceeds about10% by weight.

[0008] For example, U.S. Pat. No. 5,112,416 discloses an aluminum-basedalloy bearing having an intermediate bonding layer where the hardness islower than 40% of the aluminum-based bearing alloy in terms of Vickershardness. While the U.S. Pat. No. 5,112,416 demonstrates a bimetalaluminum bearing, there is no disclosure that such could operate underhigh load, high fatigue conditions. The highest known fatigue strengthshown by any prior bi-metal aluminum bearings is less than 90 megapascals.

SUMMARY OF THE INVENTION

[0009] A sliding bearing constructed according to the invention has asteel backing on which a bi-metal lining is bonded. The lining includesan aluminum-based bearing layer and an intermediate layer ofaluminum-based metal disposed between the bearing layer and the steelbacking. The composite bearing material exhibits a fatigue strength ofat least 90 MPa.

[0010] The invention has the advantage of providing a bi-metal aluminumbearing with a fatigue strength at a level normally associated withtraditional trimetal bearings.

[0011] The bearing material has the further advantage of providing analuminum-based bearing layer that has a fine microstructure; therebyimproving the fatigue strength of a bearing produced from the compositebearing material.

[0012] There is also disclosed a method of manufacturing a compositebearing including the steps of: a) casting an aluminum alloy to producean aluminum-based bearing layer having silicon particles of less than 4microns in average diameter dispersed uniformly therein, and a softphase having a maximum length of 250 microns; b) cladding analuminum-based intermediate layer material to said aluminum-basedbearing layer to produce a bi-metal lining; and c) hot bonding a steelbacking layer to said bi-metal lining.

THE DRAWINGS

[0013] These and other features and advantages of the present inventionwill become more readily appreciated when considered in connection withthe following detailed description and drawings, wherein:

[0014]FIG. 1 is a micrograph demonstrating the fine microstructure ofthe aluminum bearing alloy;

[0015]FIG. 2 is a micrograph demonstrating the fine microstructure ofthe aluminum bearing alloy of the present invention;

[0016]FIG. 3 is a micrograph showing the various layers of the compositebearing material of the present invention;

[0017]FIG. 4 is a micrograph detailing the silicon particles dispersedwithin the aluminum bearing alloy of the present invention;

[0018]FIG. 5 is a view of an apparatus utilized to produce the aluminumbearing alloy of the present invention;

[0019]FIG. 6 is a view detailing an apparatus that is used for claddingan aluminum intermediate layer with an aluminum bearing layer of thepresent invention; and

[0020]FIG. 7 is a view detailing a testing apparatus for determining thefatigue strength of a bearing.

DETAILED DESCRIPTION

[0021] With reference to FIG. 3, there is shown a preferred embodimentof the composite bearing material 5 of the present invention. Thecomposite bearing material 5 includes an aluminum-based bearing layer10, a steel backing 15, and an intermediate layer 20 positioned betweenthe aluminum layer 10 and the steel backing 15.

[0022] The aluminum-based bearing layer 10 preferably has a compositionincluding: 4 to 15 weight percent lead or tin, 2 to 6 weight percentsilicon, and up to 2 percent by weight of an element selected from thegroup consisting of manganese, magnesium, nickel, zirconium, zinc,copper, or chromium; the remainder of the aluminum bearing layer is purealuminum. In a preferred embodiment, the aluminum-based bearing layer 10includes 8 weight percent tin, 3 weight percent silicon, 2 weightpercent lead, 0.8 weight percent copper, 0.2 weight percent chromium,with the remainder being aluminum. In a second embodiment, thealuminum-based bearing layer includes 6 weight percent tin, 4 weightpercent silicon, 0.8 weight percent copper, with the remainder beingaluminum.

[0023] Regardless of the exact composition of the aluminum-based bearinglayer 10, the aluminum-based bearing layer 10 is characterized in thatit has a fine microstructure. Aluminum materials having a finemicrostructure, as well as methods of their production are disclosed inU.S. Pat. Nos. 5,536,587; 5,365,664; and 5,053,286, which are hereinincorporated by reference. A fine microstructure with reference to theconstituents of the aluminum-based bearing material 10 is characterizedby silicon particles having an average diameter of 4 microns or lessuniformly dispersed within an aluminum matrix, as well as soft phaseparticles of less than 250 microns in length.

[0024] In a preferred embodiment, the aluminum-based bearing layer 10 iscast on a twin roll-casting machine, which imparts a fine microstructureto the alloy. The process of the preferred embodiment involves casting athin strip of aluminum alloy between two water-cooled rolls at athickness of from 1 to 10 millimeters, and preferably between 4 and 7millimeters. The rate of heat removal from the aluminum alloy includes atemperature drop from about 700° C. to a temperature below 300° C. inless than 2 seconds, and preferably less than 1 second.

[0025] The microstructure obtained when the aluminum-based bearing layer10 is cast with such a high rate of cooling is shown in FIGS. 1 and 2.The extremely fine microstructure imparts a high strength to thealuminum-based bearing layer 10. The aluminum-based bearing layer 10 hassilicon particles 12 that are dispersed within the aluminum matrix 14and have an average size of less than 4 microns in diameter.Furthermore, the maximum length of the soft phase product particles,i.e., the lead or tin is preferably less than 250 microns in size, andeven more preferably, less than about 10 microns or less in length. Thefine size of the silicon and other constituents imparts a very highfatigue resistance to the aluminum-based bearing layer 10 of the presentinvention.

[0026] The intermediate layer 20 of the present invention is preferablypure aluminum or an aluminum alloy that has a lower yield strength thanthe aluminum-based bearing layer 10. The intermediate layer 20 is sizedsuch that it has a thickness of at least 60 micrometers and preferablybetween 60 and 120 micrometers after being processed.

[0027] There is also disclosed a method of manufacturing a compositebearing including the steps of: a) casting an aluminum alloy to producean aluminum-based bearing layer having silicon particles of less than 4microns in an average diameter dispersed uniformly therein, and a softphase having a maximum length of 250 microns; b) cladding analuminum-based intermediate layer material to said aluminum-basedbearing layer to produce a bi-metal lining; and c) hot bonding a steelbacking layer to said bi-metal lining.

[0028] As referenced above, the aluminum-based bearing material 10 iscast in a water-cooled twin roll casting process that produces a veryfine microstructure. The aluminum-based bearing material 10 is castgenerally with a thickness of 3 to 7 millimeters and at a rate of 70 to125 centimeters per minute. In the water-cooled twin roll castingprocess, the molten alloy is introduced between the rolls at a pointabove the centerline of the two rolls. With reference to FIG. 5, thereis shown an apparatus for casting the aluminum-based bearing layer 10 inaccordance with a preferred embodiment of the present invention. Themolten aluminum alloy is supplied to a crucible 21 that has a slip-likedischarge nozzle 22 located between two rotating rolls 25, 27. Eachrotating roll 25, 27 has an array of internal coolant channels orpassages 30 located in close proximity to a relatively thin metal shell32. Each shell 32 is preferably formed of copper or other metal having ahigh thermal conductivity, whereby the shell 32 material is able totransmit heat from the molten aluminum alloy to the coolant passingthrough the channels 30. Copper and copper alloys are chosen for theirhigh thermal conductivity; however, steel, brass, aluminum alloys, orother materials may also be used for the shell material 32. The castingsurfaces should be generally smooth and symmetrical to maximizeuniformity in strip casting. Water is used as a heat transfer medium dueto its high heat capacity, low cost and ready availability. The aluminumalloy is rapidly cooled from the molten state to the solid state in ashort time period, such as less than one second. The internally cooledrolls 25, 27 are continuously driven in the directions indicated bynumerals 41 and 43 such that the freshly cooled roll surfaces are beingcontinuously replenished in crucible 21 to maintain an essentiallyconstant hydrostatic head on the molten material being dischargedthrough the nozzle slit 22. The cooled and solidified alloy emerges fromthe rolls as a continuous solid strip 45 having a thickness dimensioncorresponding to the spacing between the opposed roll surfaces. Thestrip material 45 can be wound on a spool for temporary storage in coilform.

[0029] After the aluminum-based bearing layer 10 is cast, theintermediate layer 20 is roll clad to the aluminum bearing layer 10. Theintermediate layer 20 is chosen such that its thickness in the finishedproduct will be between 60 and 120 micrometers. As referenced above, apreferred intermediate layer 20 material includes pure aluminum or analuminum alloy.

[0030] After the intermediate layer 20 has been clad to thealuminum-based bearing layer 10, the bi-metal lining is hot bonded tothe steel backing 15 according to the process disclosed in U.S. Pat. No.3,078,563, which is herein incorporated by reference. In this process,the temperature of the components to be bonded is raised significantlyabove ambient temperature, and the aluminum-based bearing layer 10 isreduced in thickness by approximately 75 percent while the reduction inthickness of the steel backing 15 is essentially zero.

[0031] With reference to FIG. 6, there is shown an apparatus utilized inthe bonding process. The bi-metal lining strip 45 is mated to a steelstrip 47 and passed through a heater. Alternatively, the steel can beheated and the bi-metal strip introduced after the heater where it isheated by the steel. The materials are kept under a non-oxidizingatmosphere to protect the strips from oxidizing while it is beingheated. The heated strips 45, 47 are passed through a rolling millassembly that includes a relatively large diameter lower roll 61 and asmaller diameter center roll 63 which is backed up by a larger diameterupper roll 65. The spacing between the rolls 61 and 63 is less than thecombined initial thicknesses of the strips 45, 47, such that thebi-metal strip 45 is compressed and reduced in thickness during thepassage of the mating strips through the rolls. The lower roll 61 ispowered to provide the force to move the strips 45, 47 through therolls. The lower roll 61 is preferably at least two times the diameterof the center roll 63 so that the center roll 63 exerts a substantiallygreater force per unit area on the bi-metal strip 45 than the unit areaforce exerted by the lower roll 61 on the steel 47. Thus, the bi-metalstrip 45 is substantially reduced in thickness whereas the thickness ofthe steel 47 remains essentially unchanged.

[0032] Because the thickness of the steel layer 47 is essentiallyunchanged, its hardness is not significantly increased, and the emergingcomposite material 5 is workable and reshapable into desired bearingconfigurations.

EXAMPLES

[0033] In a bearing fatigue test widely utilized in the engine bearingindustry, the composite material is tested in the form of a bearing in ahydraulic-bearing fatigue test machine, depicted in FIG. 7. The testbearing 73 is carried in a connecting rod 72 on an eccentric portion 71of a shaft 70 which is rotating at an RPM typically seen by the bearingin actual use. On the other end of the connecting rod 72, there is apiston 74 in a hydraulic cylinder. Reciprocation of the connecting rod72 and piston 74 is resisted by the oil in the hydraulic cylinder. Thedegree of resistance and the load on the bearing is determined by anadjustable valve 75 on the cylinder. The load is measured by a straingage 76 on the connecting rod 72.

[0034] Testing begins at an arbitrary load selected by the researchers.The test is run for seven million cycles and the bearing is inspectedfor fatigue. If fatigue is present, the test is recorded as a failureand the next test is run at a lower load. If fatigue is not present, thetest is recorded as a run out and the next test is run at a higher load.After multiple tests, the data is analyzed statistically and an averagefatigue load is determined. Results of the test are shown in the tablesbelow. Table 1 identifies two embodiments of the composite bearingmaterial of the present invention. Table 1 includes the relativecomposition of the bearing material with the numbers following theelements indicating a weight percent of that element, as well as theinterlayer thickness in microns, the interlayer type, the bonding methodutilized to bond the alloy material to a steel backing, the bearingalloy microstructure, as well as the fatigue strength determined by thetests. For comparison, Table 2 identifies corresponding properties andcharacteristics of know prior bi-metal aluminum bearings. TABLE 1Interlayer Alloy Fatigue Bearing Thickness, Interlayer Bonding Micro-Strength, Alloy Composition Microns Type Method structure MPa Al Sn8 Si3Pb2 Cu0.8 Cr0.2 100 Pure Al Hot Fine 100 Al Sn6 Si4 Cu0.8 100 Pure AlHot Fine 100

[0035] TABLE 2 Interlayer Alloy Fatigue Bearing Thickness, InterlayerBonding Micro- Strength, Alloy Composition Microns Type Method structureMPa Al Sn8 Si3 Pb2 Cu0.8 Cr0.2 None N/A Hot Fine 74 Al Sn12 Si3 Pb2Mn0.2 Sb0.2 40-50 “Reinforced” Warm Medium 87 Al Sn10 Si2 Pb1 Mn0.2Sb0.2 <20  Nickel Warm Medium 68 Al Sn10 Ni2 Mn1 35 Pure Al Warm Coarse76 Al Sn11 Si3 Pb1 Cu0.9 Cr0.2 <10  Nickel Warm Medium 78 Al Sn10 Si3Pb2 Cu0.9 Cr0.2 50 Pure Al Warm Medium 74 Al Sn11 Si4 Cu1 50 Pure AlWarm Coarse 50 Al Sn11 Si4 Cu2 <10  Nickel Warm Fine 72 Al Sn12 Si3 Pb2Mn0.2 Sb0.2 40 Pure Al Warm Medium 75 An Sn20 Cu1 40 Pure Al Cold Coarse53 Al Sn8 Si3 Pb2 Cu0.8 Cr0.2 None None Hot Coarse 41 Al Sn8 Si3 Pb2Cu0.8 Cr0.2 75 Pure Al Hot Coarse 57

[0036] As can be seen from a comparison of the above tables, thecomposite bearing material of the invention has a fatigue strength of100 mega pascals which exceeds that of all known prior art bi-metalaluminum materials.

[0037] Obviously, many modifications and variations of the presentinvention are possible in light of the above teachings. it is,therefore, to be understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed. The invention is defined by the claims.

1. A sliding bearing comprising: a steel backing; and a bi-metal liningbonded to said steel backing including a bearing layer of aluminum-basedmetal and an intermediate layer of aluminum-based metal disposed betweensaid steel backing and said bearing layer, said bi-metal aluminum lininghaving a fatigue strength exceeding 90 MPa.
 2. The sliding bearing ofclaim 1 wherein said fatigue strength is about 100 MPa.
 3. The slidingbearing of claim 1 wherein said bearing layer comprises a chill castaluminum-silicon based alloy.
 4. The sliding bearing of claim 1 whereinsaid bearing layer comprises an alloy of aluminum-lead-silicon.
 5. Thesliding bearing of claim 1 wherein said bearing layer comprises an alloyof aluminum-tin-silicon.
 6. The sliding bearing of claim 1 wherein saidbearing layer includes a dispersion of silicon particles having anaverage particle size less than 4 microns in diameter.
 7. The slidingbearing of claim 1 wherein said intermediate layer has a thickness of atleast 60 microns.
 8. The sliding bearing of claim 7 wherein saidthickness of said intermediate layer is between about 60 to 120 microns.9. The sliding bearing of claim 1 wherein said bearing layer and saidintermediate layer each have a yield strength, said yield strength ofsaid intermediate layer being less than said yield strength of saidbearing layer.
 10. The sliding bearing of claim 1 wherein said bearinglayer has a chill cast microstructure and is roll bonded to saidintermediate layer.
 11. The sliding bearing of claim 1 wherein saidbearing layer includes an amount of silicon ranging from about 2 to 6weight percent and a soft phase of either tin or lead present in anamount of from 4 to 15 weight percent.
 12. The sliding bearing of claim1 wherein said soft phase ranges from about 6 to 10 percent by weight.13. The sliding bearing of claim 1 further including up to 2 percent byweight of an element selected from the group consisting of: Mn, Mg, Ni,Zr, Zn, Cu, Cr.
 14. A composite bearing material comprising: analuminum-based bearing layer; a steel backing; and an intermediate layerhaving a thickness of from 60 to 120 micrometers positioned between saidaluminum-based bearing layer and said steel backing, said aluminum-basedbearing layer having silicon particles of less than 4 microns in averagediameter dispersed uniformly therein, and a soft phase having a maximumlength of 250 microns.
 15. The composite bearing material of claim 14wherein said soft phase has a length of 10 microns or less.
 16. Thecomposite material of claim 15 wherein said soft phase comprises lead ortin.
 17. The composite bearing material of claim 15 wherein saidaluminum-based bearing layer comprises: 4 to 15 percent by weight softphase; 2 to 6 percent by weight Si; up to 2 percent by weight of anelement selected from the group consisting of: Mn, Mg, Ni, Zr, Zn, Cu,Cr; the remainder Al.
 18. The composite bearing material of claim 14wherein said aluminum-based bearing layer comprises: 8 percent by weightSn; 2 percent by weight Pb; 3 percent by weight Si; 0.8 percent byweight Cu; 0.2 percent by weight Cr; the remainder Al.
 19. The compositebearing material of claim 14 wherein said aluminum-based bearing layercomprises: 6 percent by weight Sn; 4 percent by weight Si; 0.8 percentby weight Cu; the remainder Al.
 20. The composite bearing material ofclaim 14 wherein said intermediate layer is formed of pure aluminum. 21.The composite bearing material of claim 14 wherein said intermediatelayer is formed of an aluminum alloy.
 22. The composite bearing materialof claim 14 wherein said composite bearing material has a fatiguestrength of at least 90 MPa.
 23. The composite bearing material of claim14 wherein said composite bearing material has a fatigue strength ofabout 100 MPa.
 24. A method of manufacturing a composite bearingcomprising the steps of: a) casting an aluminum alloy to produce analuminum-based bearing layer having silicon particles of less than 4microns in average diameter dispersed uniformly therein, and a softphase having a maximum length of 250 microns; b) cladding analuminum-based intermediate layer material to said aluminum-basedbearing layer to produce a bi-metal lining; c) hot bonding asteel-backing layer to said bi-metal lining.
 25. The method ofmanufacturing a composite bearing of claim 24 wherein a temperature ofsaid aluminum alloy is reduced from 700° C. to less than 300° C. in lessthan 2 seconds in said casting step.
 26. The method of manufacturing acomposite bearing of claim 24 wherein during the hot bonding step athickness of the aluminum-based bearing layer is reduced by 60 to 80percent.
 27. The method of manufacturing a composite bearing of claim 27wherein a thickness of said steel backing is unchanged.